Field of the Invention
The present invention relates to a technique of controlling operation of a generator and an internal combustion engine mounted on a hybrid vehicle.
Description of the Related Art
Among hybrid vehicles developed in recent years, there is known a type which comprises an engine (internal combustion engine), a generator driven by the internal combustion engine to generate electricity, a traction battery chargeable by electricity supply from the generator, and a traction motor supplied with electricity from the traction battery or the generator to drive drive-wheels.
In hybrid vehicles of this type, electricity generated by the generator is supplied to the traction battery and the traction motor. In vehicle deceleration, electricity is generated by regenerative braking using the traction motor, wherein the generated electricity can be supplied to the traction battery for charging.
Further, as shown in Japanese Unexamined Patent Application Publication No. 2014-121963, hybrid vehicles capable of switching between EV mode, series mode and parallel mode have been developed. In parallel mode, the vehicle is driven by both the internal combustion engine and the motor. Parallel mode is thus used, for example in high-speed traveling requiring high output.
Among vehicles provided with parallel mode, there are vehicles in which, when the output torque required of the internal combustion engine exceeds an appropriately-predetermined electricity-generation upper limit torque during traveling in parallel mode, control is performed to stop electricity generation by the generator while causing the internal combustion engine to continue driving the drive wheels. Stopping the electricity generation this way can suppress load on the internal combustion engine, thereby reducing fuel consumption.
However, when the electricity generation by the generator is stopped because the output torque required of the internal combustion engine exceeds the electricity-generation upper limit torque during high-load traveling in parallel mode, SOC of the traction battery decreases due to electricity consumption by the traction motor. There is therefore a problem that when high-speed traveling continues for a long time, the traction battery experiences a great decrease in SOC.